Jellyfish have been around for at least 500 million years, older than dinosaurs and even trees. Over millions of years, they and other plants and animals evolved into precisely calibrated and balanced parts of an ecological tapestry. As humans continue to disrupt these interdependent relationships, we are seeing profound effects on our environment and on human life.
Jellyfish are not without their benefits. They provide food, create shelter for juvenile fish in their tentacles, and the green fluorescent protein responsible for their bioluminescence, their toxins, and their tissues are being studied for medical uses. But a surge in the number of this brainless, spineless, eyeless, bloodless creature in coastal waters has become a new threat to fisheries around the world for over the last decade. In the thickest spots there may be more jellyfish than there is water, making seas around the world turning into jellyfish soup, as swarms of the creatures hit coastal areas, paralyzing power plants and undermining fisheries. In places like Sweden, Israel, the US and the Philippines, power plants have been affected by blooms of jellyfish. They clog cooling water intakes at power plants, causing power reductions or shutdowns. Jellyfish blooms also disrupt the fishing industry by tearing nets and harming fish. Their tentacles can enter aquaculture pens and suffocate the fish thereby reducing the catch of fishermen.
Jellyfish populations are normally held in check by fish, mostly because these two groups compete for the same food sources. However, overfishing in many parts of the ocean has led to increasing jellyfish populations. Jellyfish may also be aided by warming ocean temperatures, which favors their development, and by the destruction of habitats of other natural predators such as turtles. Since the 1990s, there have been jellyfish problems in the East China and Yellow Seas, the Northern Benguela Current off Namibia, the Black Sea, the Baltic Sea, coastal Middle Eastern waters, and off the coasts of Spain and France. But the most dramatic of these outbreaks is in Japanese waters where the giant Nomura’s jellyfish has increased significantly, wreaking havoc with fisheries. The name “Nomura” is given to this jellyfish in honor of Kanichi Nomura, director general of the Fukui Prefecture Fisheries Experiment Station who in 1921 sent a specimen of Nomura jellyfish to Kamakichi Kishinouye, a marine animal researcher who later succeeded in identifying the creature and determined its scientific classification in 1922.
Physically, apart from their enormous size which can grow up to 2 m in diameter and 200 kg in weight, Nomura are basically not much different from jellyfish in general. About 94% substance of their body is water and they experience three forms in its life cycle: the planula, the polyp, and the medusa form. The cycle begins when the mother releases eggs & sperm into the high seas, which then coalesce into planula larvae. The planula then attaches itself to the seabed and turns into a polyp which initially measures only a few millimeters. The polyp form resembles a miniature sea anemone. During this stage, which can last for several months or years, asexual reproduction occurs. The polyps clone themselves and bud into another stage of jellyfish life, called ephyra. It is this form that grows into the adult medusa jellyfish. Jellyfish polyps can choose to undergo 2 kinds of life paths: remain as polyps or go into the formation phase of adult jellyfish medusa.
Nomura actually has a cycle of its own. They appear on the beach once every 20 years, but in recent years the cycle has become chaotic, which has ultimately troubled Japan, if not the world. Before 2000, Nomura’s jellyfish blooms occurred in 1920, 1958, and 1995 in Asian waters. But since 2002, the blooms have occurred almost every year, with particularly large ones in 2005 and 2009. Because of their size, Nomura consume massive amounts of zooplankton, depleting this vital part of the food chain for other organisms. A particularly large Nomura’s jellyfish takes in enough seawater each day to fill a swimming pool, gobbling up any plankton it catches in the process. Plankton is also the prey of juvenile sardines and horse mackerel. The overfishing of such species is believed to be one cause for the proliferation of this jellyfish. Another key threat of the Nomura’s derives from the fact that this jellyfish reproduces extremely rapidly. A mature jellyfish has the ability to produce billions of eggs at a time, and they can do this when they are attacked. Once fertilized, these eggs develop into a resting polyp stage that also has the ability to multiply rapidly, effectively carpeting areas of the seafloor.
There have been no confirmed swarms of Nomura’s jellyfish reaching Japan in the past year or two, but it is too early for the country to let down its guard. Juvenile jellyfish can remain in a form of suspended development covered by stiff shells for eight years or so. China’s embankments are home to an astronomical number of these giants-to-be, and any stimulus could cause them to awake en masse.
It is easy and compelling to draw a direct link from human activity to increasing jellyfish populations. In their blind simplicity and poisonous beauty, jellyfish are hailed to be unstoppable in the face of ecological destruction. Recent reports of other jellyfish blooms are being reported in many other parts of the ocean. In the Gulf of Mexico, for example, the last thirty years populations of two species of jellyfish, the sea nettle, and the moon jellyfish, has exploded especially in dead zones as these are one of the few organisms that can tolerate hypoxia. Jellyfish in the Gulf now swarm over hundreds and perhaps even thousands of square miles each summer. As in Japanese waters, the causes of outbreaks in other seas are believed to be coastal development, nutrient enrichment, overfishing of commercial fish species, global warming and so on. Enormous blooms of jellyfish around the world may be the wake-up call humanity needs if it is to stop destroying marine ecosystems. There is little we can do now to curb jellyfish blooms, except to take better care of our oceans. Monty Graham, senior marine scientist at the Dauphin Island Sea Lab in Alabama, said, “If ecosystems are healthy, then jellies will do their normal thing…But if you nudge the system towards the more perturbed side, the jellyfish will take off, and so we do sort of think of jellies as that kind of canary, that bellwether of change.” Jellyfish blooms are likely the result of just one of countless ecological niches human have unraveled. Who knows what other havoc human actions will set in motion?